No, PMDD does not cause heavy periods. PMDD is a malfunction in the brain which causes an abnormal negative reaction to the normal hormone fluctuations. PMDD does not affect the amount of blood loss you experience.
Symptoms of PMDD
Feelings of sadness or despair or even thoughts of suicide
Feelings of tension or anxiety
Panic attacks, mood swings, or frequent crying
Lasting irritability or anger that affects other people
Lack of interest in daily activities and relationships
Trouble thinking or focusing
Tiredness or low-energy
Food cravings or binge eating
Feeling out of control
Physical symptoms, such as bloating, breast tenderness, headaches, and joint or muscle pain
These symptoms occur during the week or two before menstruation and go away within a few days after bleeding begins. A diagnosis of PMDD requires the presence of at least five of these symptoms. You can read more here:
Heavy periods, however, could be associated with other symptoms, such as pelvic pain or painful periods, that could exacerbate the mood symptoms associated with PMDD. Underlying medical conditions (such as thyroid disorders) could be associated with both heavy or irregular periods as well as mood symptoms. Heavy periods could also suggest an underlying hormonal problem such as irregular ovulation, a hormone imbalance, or an abnormal growth in your uterus (such as polyps, fibroids, or a tumor). Heavy periods should be discussed with an OB/GYN or primary care provider.