The main alkaloid in Datura inoxia seeds it scopolamine. The alkaloid makeup is nearly 97% scopolamine. So it's very similar to taking pure scopolamine. The only difference really is that the potency varies from seed to seed.
The average seed contains about 0.4% scopolamine. This data below is based on an average seed size of average potency.
1 seed would weigh about 10 mg and contain about 40 micrograms of scopolamine.
10 seeds would weigh about 100 mg and contain about 400 micrograms of scopolamine.
20 seeds would weigh about 200 mg and contain about 800 micrograms of scopolamine.
25 seeds would weigh about 250 mg and contain about 1000 micrograms of scopolamine.
37.5 seeds would weigh about 375 mg and contain about 1500 micrograms of scopolamine.
250 seeds would weigh about 2500 mg and contain about 10,000 micrograms of scopolamine.
The adult scopolamine dose needed for medicinal effects lies between 100 and 1000 micrograms.
The adult scopolamine dose needed for mental intoxication lies between 1000 and 1500 micrograms.
The adult scopolamine dose needed for delirium lies between 1500 and 10,000 micrograms.
The adult scopolamine dose needed to end your life is about 10,000 micrograms or more. But it may be less in some people.
Doctors routinely prescribe scopolamine for many things in the dosage range of 400-800 micrograms. 1500 micrograms is considered the maximum safe dose of scopolamine. 10,000 micrograms can be lethal. Anything below 400 micrograms (10 seeds) is extremely safe and effective for boosting the effects of other psychedelics. A larger dose is not needed.
You should always assume you have super potent seeds and that you are extra sensitive to the effects of scopolamine. Those figure above are average figures. Some seeds are super potent and extra large. Dosing by seed count is not wise. Doses should be weighed in milligrams.