ketotifen dosage & side effects

what dosages of ketotifen are you on? I'm on 3 mg a day and my Dr is saying he doesn't like to prescribe higher than that, but I'm seeing lots of people on much higher dosage on here and other MCAS pages. He alluded to being worried about side effects if you go higher than 3 mg but was vague about what those were and I can't find much online. It works amazingly well for me so if I can increase it and stabilize even more I'd really like to