St. John’s Wort causes drowsiness in roughly 5 to 10 percent of people who take it, making tiredness a real but relatively uncommon side effect. That rate is significantly lower than what you’d expect from prescription antidepressants, where 20 to 30 percent of users report drowsiness. So while the herb can make some people feel tired, most users don’t experience it.
Why It Can Cause Drowsiness
St. John’s Wort contains an active compound called hyperforin that influences several chemical messenger systems in the brain at once. One of those systems involves GABA, the brain’s primary calming signal. Hyperforin slows the reabsorption of GABA after it’s released, which means more of it stays active between nerve cells for longer. The herb also binds directly to two types of GABA receptors, the same docking sites targeted by anti-anxiety medications like benzodiazepines. In animal studies, this GABA activity produces a measurable anxiety-reducing effect.
That calming action is part of what makes the herb helpful for mood, but in some people it tips over into noticeable sleepiness. The effect is dose-dependent, meaning higher amounts are more likely to cause it. St. John’s Wort also influences serotonin, dopamine, and norepinephrine reuptake simultaneously, and this broad neurochemical activity is why individual responses vary so much. Some people feel more alert as their mood improves, while others notice a sedating quality, especially in the first few weeks.
How It Compares to Antidepressants
If you’re weighing St. John’s Wort against a prescription antidepressant, the sedation profile is notably different. A large reanalysis of four controlled clinical trials compared a standardized St. John’s Wort extract to paroxetine (a common SSRI). The herbal extract produced adverse event rates comparable to placebo and was, in the researchers’ words, “devoid of effects of sedation” at the group level. Paroxetine, by contrast, caused adverse events at rates 10 to 38 times higher across most symptom categories, including drowsiness, digestive problems, and sexual dysfunction.
Excessive sedation, the kind where you feel genuinely unable to stay awake, occurs in fewer than 5 percent of St. John’s Wort users. With sedating antidepressants, that figure rises to 10 to 20 percent. This doesn’t mean the herb is side-effect-free, but tiredness is less likely and usually milder than what prescription options produce.
Effects on Sleep Quality
One common concern is whether St. John’s Wort disrupts your sleep in a way that leaves you groggy during the day. Placebo-controlled studies in healthy adults found that the herb increases REM sleep latency, meaning it takes longer to enter the dreaming phase of sleep after you fall asleep. This is actually a pattern shared by most antidepressants. However, it did not change total sleep duration or other aspects of sleep structure, so it’s unlikely to cause the kind of broken or shallow sleep that leads to next-day fatigue.
There’s also no evidence that St. John’s Wort raises melatonin levels. A study measuring both salivary melatonin and a urinary melatonin marker found no change after treatment. So the tiredness some people feel isn’t coming from a spike in your body’s sleep hormone. It’s more likely tied to the GABA and serotonin effects described above.
When Tiredness Is More Likely
A few situations increase your chances of feeling drowsy on St. John’s Wort:
- The first few weeks. Side effects, including tiredness, are most common early in treatment as your brain adjusts to the shift in neurotransmitter activity. Many people find that drowsiness fades after two to four weeks.
- Higher doses. Standard dosing is typically 300 mg three times daily of a standardized extract. Taking more than that raises the probability of sedation.
- Combining it with other sedating substances. Taking St. John’s Wort alongside narcotic painkillers can amplify both the sedating and pain-relieving effects of those drugs. Alcohol, sleep aids, and antihistamines can also compound the drowsiness.
Managing Tiredness While Taking It
If you’re experiencing drowsiness but want to continue taking St. John’s Wort, the simplest adjustment is shifting your dose to the evening. Since the herb doesn’t disrupt overall sleep architecture, taking it closer to bedtime lets the sedating window overlap with hours you’d be asleep anyway. Some people split their dose so that a smaller amount is taken in the morning and a larger portion at night.
Giving it time also helps. Because the tiredness often reflects your brain’s initial adjustment rather than a permanent effect, waiting two to three weeks before deciding to stop can be worthwhile. If drowsiness persists beyond that window or interferes with driving or work, it’s a sign the herb may not be the right fit for you. Individual brain chemistry varies enough that a side effect affecting fewer than one in ten people can still be your consistent experience.