I don't turn anyone away for being on medication. Still, what you come to the session with does make a difference.
Why some substances dampen trance
Anything that acts directly on the central nervous system also changes how accessible you are to suggestion. On strong psychiatric medication — high-dose sedatives, some antipsychotics, benzodiazepines — many clients respond noticeably more dampened: the trance still happens, but it's flatter, and the emotional involvement is smaller. With lower-dose antidepressants I see this far less in practice — most clients on an SSRI, for example, work perfectly normally, with no difference I can notice.
Illegal drugs and alcohol affect the outcome in a similar way, usually depending on the dose. If someone is at their usual "working level" of being slightly drunk, it's often still fine to work with. Heavier intoxication makes it difficult — not because anything dangerous happens, but because the conscious mind is too distracted to carry the session. We'd end up spending a lot of time without anything sticking afterward.
What this means for your session
As a general rule: if it's possible for you, come to the session sober — hypnosis works more directly that way, and we get to something you can actually take with you faster.
If you're on prescribed medication — for anxiety, depression, or sleep problems, say — that doesn't automatically mean hypnosis works worse for you. It just means we talk about it openly beforehand, so I know what I'm working with and can adjust the suggestions accordingly. One thing matters to me here: never stop your medication on your own just because a session felt good. Whether and how a dose gets changed is a decision you make together with the prescribing doctor — not based on a single hypnosis session.
For some concerns the starting point is different to begin with: with medication addiction, for example, we work directly with the dependency on the substance itself, not despite it — there, the medication use isn't the obstacle, it's the subject of the session.