Mood medicine works, and it can also be undone by ordinary food and by a supplement you bought for something else. That is the part people miss. A herb for low mood can make your antidepressant stop working. A glass of grapefruit juice can make a drug level double. A piece of aged cheese can send your blood pressure soaring if you are on the wrong drug. These are not rare reactions. They are pharmacology, and they are predictable once you know the mechanism.

The main mechanism is CYP3A4, a liver enzyme that breaks down about half of all prescription drugs. Some foods and herbs block it, so drug levels go up. Some induce it, so drug levels go down. Both directions can hurt you.

St John's wort is the biggest inducer. It induces CYP3A4, which lowers levels of many drugs, including hormonal contraceptives, which can lead to breakthrough bleeding and unintended pregnancy, statins, blood thinners, transplant drugs, and HIV drugs. It also adds serotonin syndrome risk with antidepressants. Serotonin syndrome is too much serotonin in the body, with headache, dizziness, sweating, agitation, tremor, high temperature, and in severe cases seizures and death. St John's wort decreases reuptake of serotonin, noradrenaline, and dopamine, so when you add it to an SSRI, SNRI, MAOI, or tramadol, you are stacking serotonin in two ways at once. The Cochrane review of 29 trials in over 5,000 patients found St John's wort superior to placebo and about as effective as standard antidepressants for mild to moderate depression, but that does not make it safe to combine. If you are on an antidepressant, do not add St John's wort without prescriber coordination. If you are not on a drug, it is still a drug interaction waiting to happen, because it can lower the level of a drug you start later.

Grapefruit is the opposite. Grapefruit juice inhibits CYP3A4 in the intestine, so more of the drug reaches the blood. Higher levels raise the risk of toxicity. The classic example is simvastatin and lovastatin, where grapefruit can raise the risk of muscle damage, myopathy and, rarely, rhabdomyolysis. The same mechanism applies to buspirone, an anti anxiety drug, where grapefruit juice raises levels, and to some calcium channel blockers, benzodiazepines, and statins. One glass is usually enough to inhibit the enzyme for a day, and the effect can last 24 to 72 hours. Seville oranges, pomelos, and limes can do a milder version of the same thing. If your drug label says avoid grapefruit, do not swap in grapefruit juice for orange juice and assume it is fine.

Tyramine is the food interaction for MAOIs, monoamine oxidase inhibitors. MAOIs block monoamine oxidase, the enzyme that normally inactivates noradrenaline, dopamine, epinephrine, and serotonin, so neurotransmitter levels rise. Tyramine is a chemical in aged, fermented, and cured foods that has sympathomimetic like effects, meaning it acts like adrenaline. Normally monoamine oxidase breaks it down. On an MAOI, it builds up, and it can trigger a hypertensive crisis, a sudden dangerous rise in blood pressure, with sweating, tremors, bounding heart rate, high blood pressure, and high temperature.

Foods high in tyramine include aged cheeses like cheddar, Swiss, and blue, smoked meats, fermented foods, pickled herring, sausage, pepperoni, soy sauce, red wine, tap beer, yeast extracts, and liver. Foods with a little tyramine include avocados, bananas, raisins, chocolate, coffee, yogurt, and cream. The rule is not to avoid all of them forever, it is to avoid high tyramine foods, eat moderate ones occasionally, and eat low ones in limited quantities, and to check with your prescriber before you change your diet. Dextromethorphan, the cough suppressant in many cold medicines, also has serotonergic effects, and with an MAOI, or within two weeks of stopping one, it can cause serotonin syndrome. OTC labels for dextromethorphan carry this warning, and people miss it because it is a cough medicine.

Lithium is a different kind of interaction, with salt, water, caffeine, and NSAIDs. Lithium levels are narrow, too low does nothing, too high is toxic. Caffeine decreases lithium levels, so if you suddenly stop coffee, lithium levels can rise. Dehydration, low salt, and NSAIDs like ibuprofen can raise lithium levels. High salt and lots of water can lower them. That is why people on lithium need regular blood tests, and why a sudden change in coffee, diet, or painkillers needs a clinician check, not a supplement.

Leafy greens and vitamin K interact with warfarin, which is not a mood drug but is often taken by people who are also on mood medicine. Vitamin K helps blood clot, warfarin thins blood, so a sudden increase in leafy greens can lower warfarin effect, and a sudden decrease can raise it. The rule is consistency, not avoidance. Eat a similar amount each week, and tell your clinician if you change your diet.

Alcohol is the interaction people underestimate most. Alcohol plus an SSRI or a benzodiazepine increases sedation, impairs driving, and worsens depression the next day. Alcohol plus metronidazole can cause a disulfiram like reaction, flushing, nausea, vomiting, abdominal cramps and headache. Alcohol plus lithium can cause dehydration and raise lithium toxicity. Alcohol is not a sleep aid, it fragments sleep, raises heart rate, and makes anxiety worse the next morning.

Caffeine interacts with mood in two ways. It blocks adenosine, which is the sleep signal, and it raises cortisol and adrenaline. If you are on lithium, caffeine changes lithium levels. If you are on an SSRI, caffeine can worsen anxiety and insomnia. If you drink coffee after noon, or more than 300 mg a day, and you feel wired at night and tired in the morning, cut back for two weeks and see what happens.

5-HTP and SAMe are supplements that also interact. 5-HTP is a direct precursor to serotonin, so it can cause serotonin syndrome when combined with SSRIs, SNRIs, MAOIs, or tramadol. SAMe is involved in methylation and monoamine synthesis, and it can trigger mania in bipolar disorder and interact with serotonergic drugs. Saffron is serotonergic too. Do not combine any of these with an antidepressant without prescriber coordination, and never stop an antidepressant abruptly to try a supplement. That can cause withdrawal and rebound, and it can make depression worse.

What I would do, before you add any supplement or change any food, is make a list. Every drug, every supplement, every herb, every tea, and how much coffee, alcohol, and grapefruit you have each week. Take that list to your prescriber or pharmacist, and ask specifically about CYP3A4, serotonin syndrome, tyramine, lithium, and warfarin. Pharmacists are the best people for this, and they will spot a combination a doctor might miss. If you start a new drug, ask the same question again, because the interaction changes with the drug, not with the food.

This is education, not medical advice. It is not a diagnosis, and it does not replace professional care. If you have signs of serotonin syndrome, like agitation, confusion, sweating, tremor, and high temperature, or signs of hypertensive crisis, like severe headache, chest pain, and very high blood pressure, get emergency help right away.

Sources: PTCB drug interactions practice, 2026. Cochrane review, St John's wort, 29 trials, over 5,000 patients.