Some call this stuff “gas station heroin” or “legal morphine.” It’s trumpeted as a relaxation drug and workout enhancer, sold as powders, teas, pills, edibles and liquid extracts, marketed as a “natural remedy” easing pain, anxiety, even opioid withdrawal. But the “natural” products can be synthetic, behave like stimulants and produce opioid-esque euphoria that devolves into rapid, wracking withdrawal, doctors say. “It’s highly addictive even for people who aren’t addicts,” said Dr. Joe Desanto, who works with several Orange County addiction treatment centers. “I’m seeing cross-trainers and athletes coming in saying, ‘What the hell is going on?’ The story starts with kratom, a tropical tree native to Southeast Asia. The culprit here is a potent derivative of kratom — 7-OH — stocked at vape shops and gas stations until California’s very recent crackdown. Now, it’s a few clicks away on the internet.…