Dosage is difficult to control.
Some undesired byproducts may be released during heating. Pills give delayed relief where as inhalers give immediate relief. Oral cannabinoids, especially in food, has unpredictable results. A medical doctor or a prescribing nurse will be much more comfortable prescribing a well-designed THC inhaler than a cannabis cigarette, tincture, or bhang, etc. Other advantages of a pharmaceutical inhaler device.