Placebo controlled double-blind study with 40 patients who have an diarrhea-predominant IBS, 20 get Neu-P11, 20 get a placebo. Neu-P11 is a, Melatonin receptor-, Serotonin 5-HT- 1A and 5-HT- 1D - agonist and a serotonin 5-HT- 2B - antagonist.

This study aims to test a possible beneficial effect of NEU-P11 in patients with IBS.

The effect on symptoms will be rated by symptom scores. The primary endpoint will be the symptomatic benefit reported by the patient answering the simple question: Did your symptoms improve compared to prior to the clinical trial.

Additional secondary endpoints will capture sleep quality, changes in stool texture and individual symptom scores employing standardized symptom scores.

The study design is a 4 week, randomised, placebo-controlled, double blind study where 40 patients receive either placebo (20) or NEU-P11 (20). In the mid of the four week time of the Study the dose can be doubled of the patient does not recognize any relief of the D-IBS.

Inclusion Criteria:

1. Subjects age 18-80 years old

2. Male or female

   Women of childbearing potential must have a negative pregnancy test at the screening visit, on Day 1 of each treatment period, and use a reliable method of contraception during the entire study duration and for at least 3 months after study drug intake. Reliable methods of contraception are:

   • oral contraception
   • Double barrier type devices (e.g., male or female condom, diaphragm, contraceptive sponge) only in combination with a spermicide.
   • Intra-uterine devices in combination with a spermicide. Abstention, rhythm method, and contraception by the partner alone are not acceptable methods of contraception. Women not of childbearing potential are defined as postmenopausal (i.e., amenorrhea for at least 1 year), or surgically or naturally sterile.

3. Subject has IBS confirmed by the Rome III diagnostic criteria

Exclusion Criteria:

1. Subject has current evidence of duodenal ulcer, gastric ulcer, diverticulitis, or infectious gastroenteritis.
2. Subject has a history of inflammatory bowel disease (e.g. Crohn's disease, ulcerative colitis, celiac disease), GI malignancy, GI obstruction, gastroparesis, carcinoid syndrome, pancreatitis, amyloidosis or ileus
3. Subject is a candidate for GI surgery or has a history of GI surgery except appendectomy and cholecystectomy.
4. Subject has psychiatric disorders which are not controlled (based on the investigator medical judgment); subject with psychosis are excluded regardless of current therapy.
5. Subject has current or recent history (within 12 months of signing on informed consent) of drug or alcohol abuse.
6. Subject is pregnant or lactating
7. Subject has history of human immunodeficiency virus (HIV) or hepatitis (B or C)
8. Subject has any condition or circumstance that could cause noncompliance with treatments or visits
9. Subject has active malignancy within the last 5 years.
10. Subject taking antipsychotic drugs, antispasmodics, antidiarrheals (e.g. loperamide, lubiprostone and bismuth subsalicylate), narcotics, prokinetic drugs, drugs indicated for IBS (e.g Alosetron), or warfarin.

Patients with diarrhea-praedominant Irritated Bowel Syndroms