Something worrisome was happening at Spurwink, a mental health clinic in Portland, Maine. Many patients being treated for opioid addiction had gone missing for days, even weeks, skipping prescription refills and therapy appointments.

The counselors feared their patients were relapsing on fentanyl. But those who reappeared did not show the telltale signs — no slurred speech, pinpoint pupils or heavy eyelids. On the contrary, they were bouncy, frenetic, spraying rapid-fire chatter, their pupils dilated. They warned of spies lurking outside the building, listening devices in ceiling tiles, worms in their throats.

In Portland, where the fentanyl can be both diluted and even costly, another drug, cheap and plentiful, has been surging to meet demand: methamphetamine, a highly addictive stimulant that electrifies the brain and grips the central nervous system.

This pretty foodie mecca has become yet another American city to be overwhelmed by meth — not the home-cooked biker party drug from the ’90s, but a far more dangerous concoction, mass-produced in Mexican cartel labs. In recent years, it has been spreading across the country, increasingly becoming a drug of first choice in many locations.

Portland’s meth onslaught came on as the city’s drug treatment community was starting to taste hope: echoing a national trend, deaths from opioids have been declining, largely because of medications that reverse opioid overdoses and those that dull cravings.