I think you're conflating two issues: self-dosage and ingestion method. Orally taken drugs, including THC, get absorbed through the intestines and filtered through the liver. The liver metabolizes a significant fraction of many drugs, including THC, which pass through it. Orally ingested THC is therefore less potent than inhaled THC, and so must be administered in correspondingly larger dosages. But nothing about oral ingestion in pill form means that the patient cannot self-dose. Just take more pills. But at least you'll know what your dosage actually is. With inhaled marijuana smoke, neither the patient nor their doctor have any way of monitoring dosage. Which just doesn't make any sense.
Not true. In fact, most doctors recommend either smoking or nebulizing to eating when possible.
First, cannabis, like most other drugs, is metabolized by the liver regardless of the ingestion method.
Second, the big difference between smoked and eaten cannabis is the speed of onset of effects. Eaten cannabis can take anywhere between 20 and 40 minutes before effects are felt. The onsent of effects for smoked or nebulized cannabis is typically less than a minute.
Third, having a pre-set dosage makes it difficult to titrate dosage by actual effects, rather than by trial and error.
So the variability of potency of crude cannabis is a red herring. It's far easier to titrate dosage when the drug can be consumed in small amounts and the effect felt almost immediately, and the effective dosage determined over a very short period of time (typically 3-5 minutes); than it is for a pre-set dosage that has to be monitored for an average of 30 minutes for each ingestion before a standard dosage is arrived at. Add to that the complication that the effective dosage will vary widely not only between people, but even from day to day. A dosage that is ideal one day may be suboptimal, or excessive, the next. Inhalation can customize the dosage extremely easily, again using smaller doses over a 3-5 minute period until the optimal effect is reached.
Add to that that the fact that cannabis is typically prescribed as an anti-nausea medication means that it many be difficult for the patient to keep the drug in their digestive system long enough to develop the desired effect. Many patients typically rely on suppository-form anti-nausea drugs because of this difficult,.
Ingestion is typically only recommended when the patient has a respiratory disorder of some sort, or when smoke or nebulized particles may be excessively irritating to the lungs (most often with the elderly).