Can I Take Glycine With Lisinopril?

Lisinopril (brand names Prinivil, Zestril) is an ACE inhibitor prescribed for hypertension, heart failure, and after myocardial infarction. Glycine is a nonessential amino acid sold as an over-the-counter powder or capsule, typically taken at bedtime for sleep or in higher daily doses for collagen and metabolic support. These are two very different classes of substance, a prescription cardiovascular drug versus a dietary amino acid, and no pharmacokinetic interaction between them is described in lisinopril's FDA labeling or in standard drug-interaction references.

The direct answer: glycine and lisinopril do not share metabolic pathways, so taking them together will not change the blood level of either substance. The relevant question is not whether they interact pharmacokinetically, they don't, based on known pharmacology, but whether glycine's own blood-pressure-lowering tendency could stack on top of lisinopril's effect in some people. That additive pharmacodynamic possibility is biologically plausible but has not been directly tested in a trial that combines the two, so the size of the risk is not established.

What the interaction databases actually say

No published trial has directly tested glycine combined with lisinopril. Standard interaction checkers and lisinopril's FDA label do not list glycine as an interacting substance. That absence reflects a lack of reported problems and a lack of dedicated study, not proof of safety in every patient. Most supplement-drug pairs share this same evidence gap: the combination has not been harmful enough, or common enough as a research question, to generate a trial.

Why "no listed interaction" is not the same as "fully studied"

Supplement-drug interaction databases are built mostly from case reports, known metabolic pathways, and manufacturer safety data. When a pairing like glycine and lisinopril has never been reported as harmful and does not share an obvious metabolic pathway, it simply does not appear as a flagged interaction. That is a meaningful data point, but it is not equivalent to a completed safety trial in patients taking both.

How lisinopril works, and where overlap could occur

Lisinopril blocks the enzyme that converts angiotensin I to angiotensin II, reducing vasoconstriction and aldosterone release. According to its FDA prescribing information, lisinopril is minimally bound to plasma proteins, is not metabolized by the liver, and is excreted largely unchanged by the kidneys (FDA label). It does not inhibit or induce cytochrome P450 enzymes or known drug transporters, so it has limited pharmacokinetic overlap with most supplements, including amino acids like glycine.

Glycine is absorbed through intestinal amino acid transporters and metabolized through the mitochondrial glycine cleavage system, a pathway unrelated to lisinopril's renal elimination. Because their absorption and clearance routes do not compete, taking them at the same time should not meaningfully change the blood concentration of either one. This is a pharmacokinetic reassurance, not a statement about combined effect.

The pharmacodynamic question: do their blood-pressure effects add up?

This is the part of the picture that is genuinely uncertain. Some published research, including animal studies and small human trials, has reported that supplemental glycine may modestly lower blood pressure, plausibly through improved nitric oxide availability or effects on vascular smooth muscle. The specific numeric effect sizes that circulate in secondary sources (particular mmHg reductions, particular study sample sizes) could not be confirmed against verified primary sources for this article and should not be treated as established facts without checking the original paper. What can be said with more confidence is the mechanism: if glycine does lower blood pressure independently, and lisinopril also lowers blood pressure by a different mechanism (blocking angiotensin II), the two effects could in theory be additive in some patients. This is a pharmacodynamic overlap, not a drug interaction in the classic sense.

No trial has enrolled patients on lisinopril and randomized them to glycine versus placebo to measure combined blood pressure change. Until that evidence exists, the additive-effect concern remains plausible rather than proven.

Glycine's other reported uses relevant to lisinopril patients

Glycine is commonly taken at 3 to 5 g before bed for sleep, based on small trials suggesting it may shorten sleep onset and improve subjective sleep quality, an effect linked to peripheral vasodilation and a drop in core body temperature. Higher daily doses (5 to 10 g or more) are sometimes used for collagen support, since glycine is a major structural component of collagen protein. Some research has also explored glycine's effect on insulin sensitivity and glutathione synthesis in people with type 2 diabetes, which is relevant because many patients on lisinopril for diabetic kidney protection also have metabolic disease. These are active areas of nutrition research rather than settled clinical guidance, and none of them change lisinopril's own indication or dosing.

Evidence-status interaction assessment: glycine plus lisinopril

A practical way to think about risk

Not every patient on lisinopril faces the same exposure to this theoretical overlap.

Lower concern: stable blood pressure on a moderate lisinopril dose, normal kidney function, and no history of dizziness or fainting with blood pressure medications. Adding glycine at a standard sleep dose (around 3 g) is unlikely to cause a noticeable problem, though a home blood pressure check in the first couple of weeks is still reasonable.

More caution warranted: higher lisinopril doses, combination antihypertensive therapy (for example lisinopril with amlodipine or a diuretic), reduced kidney function, or a personal history of orthostatic hypotension. In this group, starting glycine at a lower dose and monitoring seated and standing blood pressure for several weeks is a sensible approach, and discussing it with the prescriber first is reasonable rather than optional.

Discuss with a prescriber before starting: anyone with a history of fainting or symptomatic low blood pressure, anyone on three or more blood pressure medications, or anyone with significantly reduced kidney function (this needs individualized clinical judgment, not a generic threshold from this article).

Kidney function matters for both substances

Lisinopril is excreted largely unchanged by the kidneys, and its half-life is prolonged in patients with reduced kidney function. Glycine is also cleared renally, and some research has reported altered plasma glycine handling in advanced chronic kidney disease, though this area is less well characterized than lisinopril's pharmacokinetics. In practice, this means patients with meaningfully reduced kidney function are the group most worth double-checking with a clinician or pharmacist before adding glycine, both because lisinopril itself needs monitoring in that setting and because clearance of the added compound is less predictable.

Dose timing

There is no pharmacokinetic reason to strictly separate the two by a set number of hours, since they do not compete for the same absorption or elimination pathways. In practice, many patients take lisinopril in the morning and glycine (if used for sleep) shortly before bed, which naturally separates the two by many hours and reduces any chance that their peak vasodilatory effects overlap. Patients taking glycine earlier in the day, for example for collagen or metabolic support, are the ones who should pay closer attention to how they feel in the hours after dosing, particularly in the first couple of weeks.

What to watch for

Anyone starting a supplement with plausible blood-pressure-lowering activity while on an antihypertensive should check blood pressure at home for a period after starting, and stay alert for dizziness on standing, lightheadedness, or visual dimming. A sustained downward trend in home readings, or any symptomatic episode, is a reason to contact the prescribing clinician rather than to adjust either the supplement or the medication independently. This is general monitoring guidance, not a substitute for individualized advice, and it does not replace an in-person evaluation if symptoms are significant or persistent.

If you are already taking both

Patients currently using glycine and lisinopril together without problems generally do not need to change anything based on the concerns above. The combination has not been shown to cause a dangerous interaction. A reasonable next step is simply to confirm your prescriber knows you take glycine, review your home blood pressure readings for any downward trend since starting it, and make sure your kidney function has been checked recently, especially if you are on a higher lisinopril dose or have other cardiovascular risk factors.

Evidence boundary

Established: glycine and lisinopril do not interact pharmacokinetically; lisinopril's clearance and metabolism are well documented in its FDA labeling and are unaffected by glycine's absorption and metabolism pathways.

Plausible but unproven: glycine may have its own mild blood-pressure-lowering effect, and this could theoretically add to lisinopril's effect in some patients, particularly those on multiple antihypertensives or with reduced kidney function.

Not established: the actual size of any combined blood-pressure effect in patients taking both, and whether glycine has any effect, positive or negative, on lisinopril's cardioprotective or kidney-protective benefits. No direct combination trial was identified to answer either question, and specific numeric claims about glycine's antihypertensive effect that circulate in secondary sources should be checked against the original study before being repeated as fact.