Everything Hurts, but Your Bloodwork Is Normal. Here's the Biological Reason.

Your COMT enzyme is responsible for breaking down catecholamines, a class of neurotransmitters that includes dopamine and norepinephrine. These chemicals don’t just affect mood; they’re also critical for pain modulation. When COMT is working normally, it keeps these neurotransmitters at a steady, balanced level so your brain can properly regulate pain signals.

The Val158Met variant in COMT is one of the most common genetic pain switches. Roughly 25% of people of European ancestry carry the homozygous slow version. If you have this variant, your COMT enzyme processes these neurotransmitters much more slowly. That means dopamine and norepinephrine stay active in your synapses longer than they should. Instead of the pain-dampening effect you’re supposed to get, you end up with constant neurochemical overstimulation that amplifies every pain signal your nervous system receives. Your brain is essentially turning the volume up on pain rather than down.

What this feels like is immediate, intense pain from minor stimuli. A light touch feels like pressure. A temperature change feels sharp. Your pain doesn’t fade quickly after an injury; it lingers and echoes. You might also notice that stimulants like coffee make your pain worse, and that quiet, low-stimulation environments help. That’s your slow COMT unable to clear the adrenaline.

Your mu-opioid receptor is the lock that endogenous opioids (your body’s natural morphine-like chemicals) fit into. When this receptor works normally, even minor pain triggers your brain to release opioids that dampen the signal. You feel hurt, but then your own opioid system kicks in and the pain fades. This is how everyone’s pain naturally resolves.

The A118G variant in OPRM1 changes the shape of this lock slightly. The G allele, carried by roughly 10-15% of people with European ancestry but up to 40% of East Asian ancestry, reduces how sensitive the receptor is to endogenous opioids. Your body is producing normal amounts of pain-relieving opioids, but your receptors aren’t responding to them as strongly, which means you have a fundamentally reduced capacity for natural pain relief. This is why opioid medications often feel ineffective for people with this variant, and why your pain seems to persist even when your body should be producing painkillers.

You likely notice that pain doesn’t resolve on its own. A minor injury that heals quickly for others causes you prolonged discomfort. Your pain tolerance is genuinely lower, and you suspect other people just don’t experience pain the same way you do. That’s correct, and it’s not psychological. Your opioid system is literally less responsive.

Your MTHFR enzyme is the critical first step in the methylation cycle, a biochemical pathway that produces neurotransmitters, repairs DNA, and generates compounds that keep your nervous system stable. One of MTHFR’s key jobs is ensuring you have enough methylated B vitamins available to build serotonin, dopamine, and other pain-modulating chemicals.

The C677T variant in MTHFR, carried by roughly 40% of people with European ancestry, reduces this enzyme’s activity by 40-70%. If you have this variant, your methylation cycle is sluggish, which means you have fewer raw materials available to build pain-dampening neurotransmitters. Your brain is trying to regulate pain with an insufficient supply of the chemicals that are supposed to do that job. You may also have elevated homocysteine, which directly increases pain signaling in your nervous system. You can eat a perfect diet and supplement aggressively with regular B vitamins and still be functionally depleted at the cellular level because your cells can’t process them efficiently.

What this means day-to-day is that pain feels sharper, more penetrating. You might also notice brain fog, mood instability, or an inability to recover well from stress. Your nervous system feels raw. Regular B vitamins don’t help much, or they help inconsistently. You’re exhausted by minimal activity.

Brain-derived neurotrophic factor, or BDNF, is a protein that shapes how sensitive your nervous system is to pain. High BDNF in your pain circuits makes pain signals louder; low BDNF makes them quieter. BDNF also affects neuroplasticity, which means it determines how easily your nervous system gets ‘stuck’ in a pain pattern after an injury. If you have high BDNF in your pain system, a minor injury can trigger a cascade that locks your nervous system into chronic pain mode.

The Val66Met variant in BDNF is carried by roughly 30% of the population. If you have the Met allele, your BDNF function is altered, and you’re more prone to central sensitization, where your nervous system essentially turns up the volume on pain signals across your entire body. Instead of pain staying localized to where it started, your whole nervous system learns to perceive pain everywhere. This is why fibromyalgia and widespread pain are so strongly linked to this variant. Your nervous system isn’t overreacting; it’s operating under a different set of neurochemical rules that make amplification the default state.

You experience pain that’s disproportionate to any injury you can identify. Pain moves around. Multiple areas hurt simultaneously. Minor irritations trigger cascades of pain. Physical therapy sometimes makes things worse because it teaches your sensitized nervous system to protect even more. You may have been told your pain is ‘all in your head.’ That’s not true; your brain is receiving genuine pain signals, but the amplification system is running at full volume.

GCH1 is an enzyme that produces tetrahydrobiopterin, or BH4, a molecule that works as a cofactor for several pain-regulating neurotransmitters, including dopamine, serotonin, and nitric oxide. When BH4 levels are adequate, your nerves can produce sufficient pain-blocking chemicals. When BH4 is depleted, your pain-regulating system fails despite adequate neurotransmitter production.

GCH1 variants, carried by roughly 15-20% of the population, reduce how much BH4 your cells can manufacture. This creates a bottleneck: you might be producing normal amounts of serotonin and dopamine, but without sufficient BH4 to activate them, those neurotransmitters can’t do their job of dampening pain signals. It’s like having a car with enough fuel but a faulty catalyst; the system can’t convert raw materials into functional output.

You likely notice that standard serotonin-boosting supplements (like 5-HTP or L-tryptophan) don’t help much, or they help inconsistently. Pain feels resistant to interventions that work for other people. You might also notice that pain is worse when you’re under stress or haven’t slept well, because those states further deplete BH4. Your nervous system is running on barely-adequate neurotransmitter reserves.

Your endocannabinoid system is your brain’s built-in pain relief mechanism. Anandamide is a neurotransmitter your body produces naturally that binds to cannabinoid receptors and dampens pain signals, reduces inflammation, and promotes nerve repair. The FAAH enzyme breaks down anandamide when you’re done using it. If FAAH works too fast, anandamide gets cleared before it can do its job. If FAAH works too slowly, anandamide lingers longer and you get sustained pain relief.

The C385A variant in FAAH, particularly the A allele carried by roughly 20-30% of the population, reduces FAAH activity. This sounds like it should be good news, but it’s complicated. People with reduced FAAH activity typically have higher baseline anandamide levels and lower baseline pain sensitivity, which is protective. However, if you have a loss-of-function FAAH variant and you also carry other pain-amplifying variants like slow COMT or BDNF Met66, the effects can interact in unexpected ways. The protective anandamide elevation may be offset by the other pain-driving variants.

If you have this variant in isolation, you probably have naturally lower pain sensitivity than average. But if you have it alongside other variants, you might not notice much benefit. You might also notice that cannabis affects you more intensely than it does others, because your endocannabinoid system is already working in overdrive.