Methamphetamine-induced vasculitis or thrombosis: Methamphetamine use is known to cause vasculitis or thrombosis, leading to erythema, pain, and potentially ulcers on the skin, especially on the lower extremities. The drug's vasoconstrictive properties can lead to reduced blood flow, resulting in tissue damage.

Cellulitis: Bacterial infection of the skin and subcutaneous tissues, which can be more common in individuals with poor hygiene, malnutrition, or compromised immune systems, often seen in drug addicts.
Abscesses or infected wounds: Methamphetamine users may have poor skin hygiene and are at risk of injecting into non-sterile sites, leading to abscess formation or infected wounds.
Thrombophlebitis: Inflammation of veins due to a blood clot, which can be caused by intravenous drug use.

Necrotizing fasciitis: A severe infection that destroys tissue under the skin, including fat and the tissue covering the muscles (fascia). It's a medical emergency that requires prompt treatment.
Deep vein thrombosis (DVT): A blood clot in a deep vein, usually in the legs, which can lead to pulmonary embolism if the clot breaks loose.
Septic emboli: Bacterial infections that can lead to the formation of emboli, which can travel to other parts of the body and cause infections in distant sites.

Erythema nodosum: An inflammatory condition characterized by the formation of nodules on the skin, often on the lower extremities, which can be associated with various conditions, including infections and drug reactions.
Polyarteritis nodosa: A condition that causes the blood vessels to swell, leading to organ damage, which can be associated with drug use in rare cases.
Leukocytoclastic vasculitis: A condition characterized by inflammation of the blood vessels, which can be caused by drug reactions or infections.