If you are new to cannabis, I recommend that you start with less than 10mg, or even 5mg of THC. You would need to look at the extract to get to the right dose. Once taken, give it at least an hour to feel the full effect (if a tincture it liquid), and longer if its an edible (up to two hours).
Once you understand how THC affects you, you can experiment with stronger dosages. Its very dependent on your individual tolerance. I personally am good for about 30mg, whereas I know others who can easily consume 100mg or more without feeling that its too strong for them.
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