Can you have both MCAS and POTS?

Yes, and it is common enough that the two plus hypermobility are frequently described together as a cluster. Co-occurrence is the expected pattern rather than a coincidence, which changes the framing from either-or to how much of each.

Does one cause the other?

That is not established. Several mechanisms have been proposed connecting mediator release to autonomic function, and proposals are not demonstrations. The honest summary is that they travel together more often than chance would predict and nobody has shown why.

How is POTS actually diagnosed?

By a sustained heart rate increase on standing, measured during a structured test, in the absence of a drop in blood pressure that would indicate something else. It is one of the few things in this whole area with a concrete measurable definition.

Why do gut symptoms show up in both?

Autonomic function affects gut motility, and mediator release affects the gut directly. So a person with either can have gut symptoms, and a person with both very often does. This is part of why the overgrowth picture overlaps with this cluster.

Which should I get checked first?

The one with a concrete test. A structured standing test is inexpensive, widely available, and gives a measurable answer, which is more than can be said for most of what is discussed in this space.

Is it MCAS or POTS?

By B. Gray Randolph · Updated August 4, 2026

Most pages framing this as a choice are asking the wrong question. These two are part of a recognised cluster, and the more useful question is how much of each is present rather than which one is real.

What actually separates them

Postural orthostatic tachycardia syndrome is defined by a measurable event: a sustained heart rate rise on standing, without the blood pressure drop that would indicate something else. Mast cell activation syndrome is defined by mediator release meeting criteria. One has a concrete bedside test. The other has two competing criteria sets that disagree about who qualifies.

That asymmetry is worth acting on. In an area where almost nothing has a clean answer, a structured standing test is inexpensive, widely available, and produces a number.

How often patients discuss both

8,976comments mention both mast cell activation and dysautonomia

out of 7,205,554 comments across 18 patient subreddits, 2011-02-24 to 2026-05-26

query: ("mcas" OR "mast cell activation") AND ("dysautonomia" OR "postural orthostatic" OR "postural tachycardia")

How this was measured, and its limits · reddit.db@a313e531

That is 11.4% of every comment mentioning dysautonomia in our corpus, the highest share of any pair we measured against that condition. In a set of 36 pairs, this one sits fourth.

Why co-occurrence is the expected pattern

These two are frequently described alongside hypermobility as a cluster that appears together more often than chance predicts. Nobody has established why. Several mechanisms connecting mediator release to autonomic function have been proposed, and a proposed mechanism is not a demonstrated one. Treat the association as real and the explanation as open.

Why gut symptoms appear in both

Autonomic function influences gut motility, and mediator release affects the gut directly. So gut symptoms are unsurprising in either, and very common in both together. That is part of why this cluster overlaps with the bacterial overgrowth picture, and why the guideline's caution applies here too.

Pimentel M et al., American Journal of Gastroenterology 2020 Clinical guideline

No single symptom can be specifically attributed to overgrowth. When three overlapping conditions all produce bloating and altered bowel habit, symptom pattern stops carrying diagnostic weight entirely.

What to do next

Get the thing that has a test tested. A structured standing test gives you a measurable result, and a measurable result is a much better foundation for a conversation with a clinician than a list of symptoms that fits four conditions.

Common questions

Can you have both MCAS and POTS?: Yes, and it is common enough that the two plus hypermobility are frequently described together as a cluster. Co-occurrence is the expected pattern rather than a coincidence, which changes the framing from either-or to how much of each.
Does one cause the other?: That is not established. Several mechanisms have been proposed connecting mediator release to autonomic function, and proposals are not demonstrations. The honest summary is that they travel together more often than chance would predict and nobody has shown why.
How is POTS actually diagnosed?: By a sustained heart rate increase on standing, measured during a structured test, in the absence of a drop in blood pressure that would indicate something else. It is one of the few things in this whole area with a concrete measurable definition.
Why do gut symptoms show up in both?: Autonomic function affects gut motility, and mediator release affects the gut directly. So a person with either can have gut symptoms, and a person with both very often does. This is part of why the overgrowth picture overlaps with this cluster.
Which should I get checked first?: The one with a concrete test. A structured standing test is inexpensive, widely available, and gives a measurable answer, which is more than can be said for most of what is discussed in this space.