I think that in general it is a very bad idea to take illegal drugs. Just because this worked for somebody else in therapy does not mean it is a good idea for you - people react differently to drugs.

It is very common to have trouble being open in session, but a good therapist will be able to help you with this. Allow it to take time. And it is possible to get prescriptions for medication that can help with anxiety - but it is less likely that you will get that kind of help if you take illegal drugs.