Diamorphine (diacetylmorphine, or heroin) is a strong opioid agonist.
The analgesic efficacy and adverse effects of oral diamorphine and morphine were equivalent in a randomized controlled trial. Diamorphine is considerably more soluble than morphine, facilitating the delivery of higher doses by subcutaneous infusion.

Pharmacology: active PO, PR, SC, IM, IV, IN, spinal and topical. Metabolized to 6-acetylmorphine and morphine. Plasma half-life: several minutes. Dduration of action: 3-4h
Indications: moderate and severe pain
Cautions: severe hepatic or renal dysfunction, other causes of severe respiratory impairment or other causes of CNS depression
Adverse effects: similar to morphine
Dose equivalence: 4-5 mg IM is equivalent to morphine 10 mg IM; 20 mg PO is equivalent to morphine 30 mg PO
Preparations: tablet, liquid, injection

Heroin is used as a recreational drug for its euphoric effects. Frequent and regular administration is associated with tolerance and physical dependence.

Woodruff R. Palliative medicine evidence-based symptomatic and supportive care for patients with advanced cancer. 4th ed. Oxford University Press, 2004. p. 126.