A few supplements have a real, if modest, evidence base for stress and anxiety, and one of them carries a safety caveat worth knowing. None of them is a substitute for addressing what is driving the stress, and if anxiety is persistent or interfering with your life, that is a conversation for your GP rather than a supplement shelf. For everyday stress, here is what the evidence actually supports.
Ashwagandha
Ashwagandha is the most-studied herb here, with reasonable evidence that it lowers subjective stress and cortisol over several weeks. The effect is real but moderate. The caveat: there have been rare reports of liver injury linked to ashwagandha, so it is best avoided if you have liver problems or take other medicines that affect the liver, and worth stopping if you notice anything like unusual fatigue, dark urine or yellowing of the skin. For most healthy people it is reasonable to try; the point is to know the flag rather than to avoid it outright.
Magnesium
Magnesium, particularly the glycinate form, is a sensible, low-risk option. The calming effect is gentle rather than dramatic, the safety margin is wide, and it doubles as a reasonable sleep aid, which matters because stress and poor sleep tend to feed each other.
L-theanine
L-theanine, the calming compound in tea, can take the edge off a racing mind without making you drowsy. It is very well tolerated and works fairly quickly, which makes it useful for situational stress rather than as a daily treatment.
An important note if you take an antidepressant
If you are on an SSRI or SNRI, some stress and mood supplements interact with it, and two (5-HTP and St John's Wort) are a genuine hard stop. Before adding anything for stress while on an antidepressant, read the SSRI guide and check the specific combination. The free checker will show you the call and the reasoning for any pair.